New York City has cleaned up its air to levels not seen in more than 50 years. And it's all happened in a short time: a 69 percent reduction in sulfur dioxide since 2008 and a 23 percent reduction in soot levels since 2007.

Have a look:

First, sulfur concentration in 2008:

And now here's what it's looked like the past year:

But how did it happen? The city has been phasing out the most polluting heating oils used in buildings. Just three years ago, the mayor's office said, 10,000 buildings were using heating oils that emit a significant amount of sulfur dioxide and, as the New York Timespoints out, more soot than all the vehicles on the city's streets and highways. Now more than half of those buildings have either switched to cleaner fuels or are actively pursuing the switch.